Systems and methods for a multiple angle light scattering (mals) instrument having two-dimensional detector array

ABSTRACT

A particle detection system uses a reflective optic comprising a curved surface to detect high angle scattered light generated by a particle in a liquid medium, when a laser beam is incident on the particle. When the particles transit the laser beam, light is scattered in all directions and is described by MIE scattering theory for particles about the size of the wavelength of light and larger or Rayleigh Scattering when the particles are smaller than the wavelength of light. By using the reflective optic, the scattered light can be detected over angles that are greater than normally obtainable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a Continuation under 35 U.S.C. 120to U.S. patent application Ser. No. 11/453,278, entitled “Systems andMethods for a Multiple Angle Light Scattering (MALS) Instrument HavingTwo-Dimensional Detector Array,” filed Jun. 13, 2006, which in turnclaims priority to U.S. Provisional Application 60/690,535, filed Jun.13, 2005, and also claims priority to and is a continuation-in-part ofU.S. application Ser. No. 11/381,346, filed May 2, 2006, which claimspriority to U.S. Provisional Application 60/676,730, filed May 2, 2005,and which also claims priority as a continuation-in-part application toU.S. patent application Ser. No. 11/231,350, filed Sep. 19, 2005. All ofthe above applications are incorporated herein in their entirety as ifset forth in full.

BACKGROUND

1. Field of the Invention

The embodiments described herein relate to identifying particles, and inparticular to identifying particles in a liquid using illuminationincident at an angle and a two-dimensional camera for capturingscattered light from the particles.

2. Background of the Invention

A major concern for, e.g., water utilities is the detection and controlof pathogenic microorganisms, both known and emerging, in potable watertreatment and distribution. There are not only a number of chlorineresistant pathogens such as Cryptosporidium that can contaminatedrinking water systems, but also potentially harmful microorganisms thatcan be introduced, either accidentally or intentionally, and propagateunder suitable environmental conditions. Due to the length of time forstandard laboratory methods to yield results, typically 24-72 hours,there has not been a reliable system to detect microbial contaminants inreal-time and on line to provide a warning of pathogen contaminationevents. Because of these expanding challenges, there has been anaccelerated development of rapid tests and real-time methods to addressthe pressing needs of the water treatment community.

Conventional microbiological methods can be used to detect some harmfulmicroorganisms; however, such methods provide limited results.Analytical methods in microbiology were developed over 120 years ago andare very similar today. These methods incorporate the following steps:sampling, culturing and isolating the microbes in a suitable growthmedia by incubation, identifying the organisms through microscopicexamination or stains, and quantifying the organisms. Cryptosporidiumand Giardia form oocysts or cysts and cannot be cultured in conventionalways. To detect these protozoan pathogens, an amount of water containingsuspected pathogens, typically 10 liters, is sent through a specialfilter to collect and concentrate the organisms. Then the filter iseluded and the organisms further processed, such as staining theorganisms and sending the concentrated solution through flow cytometry,for example. These procedures, which can be found in Standard Methods orASME, require ascetic technique in sampling and handling, skilledtechnicians to perform the analysis, and a number of reagents,materials, and instruments to obtain results. Practically, such methodshave, therefore, proved to be time consuming, costly, and of littleeffectiveness for many current environmental field applications.

In order to reduce the amount of time to access microbiological results,a number of methods have been developed, mostly in the field ofmedicine. These faster tests have been improved and adapted to theenvironmental field and are generally categorized as 1)accelerated/automated tests 2) rapid tests and 3) contamination warningsystems (CWS).

Accelerated tests are by grab sample and results can be obtained in 4hours to 18 hours. Accelerated tests include immunoassays, ATPluminescence, and fluorescent antibody fixation. Rapid tests are also bygrab sample and require manipulation of the sample to ‘tag’ the microbeswith an identifiable marker or concentrate the microbe's geneticmaterial (DNA) for subsequent identification. Results are normallyavailable in 1-3 hours. These types of tests include Polymerase ChainReaction (PCR) and Flow Cytometry.

Real-time contamination warning systems are continuous warning devicesthat detect contaminants and provide an ‘event’ warning within minutesto prompt further investigation or action. CWS include laser-basedmulti-angle light scattering (MALS) and multi-parameter chemical &particle instruments that detect water quality changes inferringpotential biological contamination. Continuous, real-time detection ofpathogens in water surveillance was first discovered in the late 1960'sand has progressed through a series of development steps until the firstpublic field demonstration in 2002.

MALS is an acronym for “multi-angle light scattering” and is based onlaser technology, photo-detection, and computer signal processing. Whencoherent light strikes a particle, a characteristic scattering patternis emitted. The scattering pattern encompasses many features of theparticle, including the size, shape, internal structures (morphology),particle surface, and material composition (organic or inorganic). Eachtype of microorganism will scatter light giving off a unique patterncalled a ‘bio-optical signature’. Photo-detectors collect the scatteredlight and capture the patterns which are then sent to an on-boardcomputer. A microorganism's bio-optical signature is then comparedagainst known pattern classifications in the detection library forresults.

Presently, a detection system capable of meeting all of the ‘idealdetection system’ parameters, e.g., as cited by the American Water WorksAssociation does not exist. Conventional MALS devices and methods oftendiffer in the amount of time to obtain results, degree of specificity,sampling frequency, concentration sensitivity, operating complexity, andcost of ownership. The events of Sep. 11, 2001, represented anescalation in the means and effects of terrorist attacks and raisedawareness of the vulnerability of major infrastructures such astransportation, finance, power and energy, communications, food, andwater. A re-examination of the security of critical assets wasinitiated, and some action has been taken in the United States toprotect our drinking water. When a water treatment system iscompromised, action needs to be taken to bring it into compliance in astimely a manner as possible. If an online MALS system is used inconjunction with other standard tests for bacteria and protozoaparasites, then the time to react is reduced and the resulting number ofpeople who could potentially get sick is reduced. In some cases, properaction can be taken even before there is any significant health risk.

SUMMARY

A particle detection system uses a reflective optic comprising a curvedsurface to detect high angle scattered light generated by a particle ina liquid medium, when a laser beam is incident on the particle. When theparticles transit the laser beam, light is scattered in all directionsand is described by MIE scattering theory for particles about the sizeof the wavelength of light and larger or Rayleigh Scattering when theparticles are smaller than the wavelength of light. By using thereflective optic, the scattered light can be detected over angles thatare greater than normally obtainable. For example, the scattered lightcan be measured through an angle 90°.

These and other features, aspects, and embodiments of the invention aredescribed below in the section entitled “Detailed Description.”

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and embodiments of the inventions are described inconjunction with the attached drawings, in which:

FIG. 1 is a diagram illustrating an example embodiment of a particledetection system;

FIG. 1A is a plot showing the orders of magnitude in detector dynamicrange required for bacterias;

FIG. 1B illustrates 2-D scatter patterns from various particles takenwith a MALS system employing a 2-D camera as disclosed herein;

FIG. 1C illustrates an exemplary layout of a preferred embodiment of the2-dimensional photodiode array;

FIG. 2 is a diagram illustrating another example embodiment of aparticle detection system;

FIG. 3A is a picture of B. suptilis spores;

FIG. 3B and 3C are pictures illustrating example optical signatures thatcan be generated by the systems of FIGS. 1 and 2 for the B. suptilisspores of FIG. 3A;

FIG. 4A is a picture of a ball of plastic spheres;

FIG. 4B and 4C are pictures illustrating example optical signatures thatcan be generated by the systems of FIGS. 1 and 2 for the ball of plasticspheres of FIG. 4A;

FIGS. 5-7 are diagrams illustrating a technique for using illuminationincident at an angle in a light scattering detection system, such as thesystems of FIGS. 1 and 2;

FIG. 8 is a diagram illustrating an example particle detection systemthat implements the technique of FIGS. 5-7 in accordance with oneembodiment;

FIG. 9 is a diagram illustrating an example particle detection systemthat implements the technique of FIGS. 5-7 in accordance with anotherembodiment;

FIG. 10 is a diagram illustrating a spectrometer ray trace for lightscattered by a particle suspended in a liquid medium and reflected by acurved mirror;

FIG. 11 is a diagram illustrating the scattered light pattern producedby the particle of FIG. 10;

FIG. 12 is a graph illustrating the relative intensity of the scatteredlight versus the scattering angle;

FIG. 13 is a diagram illustrating a system configured to collect lightscattered by a particle and reflected by a curved reflective optic asdescribed herein; and

FIG. 14 is a diagram illustrating an example detector system, such as a2-dimensional photodetector camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, all numbers disclosed herein areapproximate values, regardless whether the word “about” or“approximately” is used in connection therewith. They may vary by up to1%, 2%, 5%, or sometimes 10 to 20%. Whenever a numerical range with alower limit, R_(L), and an upper limit R_(u), is disclosed, any number Rfalling within the range is specifically and expressly disclosed. Inparticular, the following numbers R within the range are specificallydisclosed: R=R_(L)+k*(R_(u)−R_(L)), wherein k is a variable ranging from1% to 100% with a 1% increment, i.e. k is 1%, 2%, 3%, 4%, 5%, . . . ,50%, 51%, 52%, . . . ,95%,96%,97%, 98%, 99%, or 100%. Moreover, anynumerical range defined by two numbers, R, as defined in the above isalso specifically disclosed. It is also emphasized that in accordancewith standard practice, various features may not be drawn to scale. Infact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

Embodiments of the present invention provide a method for real-timeparticle detection that uses advancements in computing power, specialoptics, photonics engineering, advanced signal processing, and complexalgorithms, in order to provide a MALS detection system that providessimplicity, cost effectiveness, speed, and reliability. The systemsdescribed in the embodiments below are analytical system using MALSwhere a side stream from a water source flows through a transparent flowcell. A laser directs a beam of light into the flow cell and through thewater stream. In certain embodiments, the water is first characterizedfor background interferences to distinguish foreign particles from thepathogens' signatures resulting in a custom detection library in eachparticular installation.

In operation, particles pass through the beam, the scattered light isemitted and captured by the detectors, converted to a digital signal,and finally sent to the computer's microbial library for analysis. Whena pattern is recognized by the library, the organisms are classifiedwithin minutes. The data can be transmitted to a user screen and remotecommunications equipment. In certain embodiments, upon reaching apre-set threshold level, an ‘alert’ can be generated and aninstantaneous sample can be automatically extracted for furtheridentification and confirmation.

Water, or other liquids for that matter, can be monitored continuouslyas it passes through the flow cell at a defined rate. This provides amuch higher probability of detecting and classifying microorganismscompared to intermittent grab samples. The speed and performance can befurther enhanced when the 1) microbial concentration level is high, 2)the water, or liquid, is of high ‘clarity’ or purity, 3) microorganismsmatch defined bio-optical signatures in the library versus an ‘unknown’,and 4) the particles are of larger size, e.g., >1 micron, givingdistinct scattering patterns.

In certain embodiments, if an unclassified organism is detected, thesystem can categorize it as an ‘unknown’ and still provide an ‘alert’ ifa certain threshold level is reached.

Thus, the systems and methods described below can provide valuable earlywarnings of potential microbial contamination. The system described canbe implemented economically and with extremely low operating costs.Further, the systems described do not use reagents or require costlyconsumables and can be compact, rugged, and easy to use, while requiringminimal operator training or expertise. In certain embodiments,‘warning’ and ‘alert’ levels can be adjusted according to therequirements of a particular implementation and can interface with anumber of communication protocols to provide immediate information forquality control or security personnel.

FIG. 1 is a diagram illustrating an example particle detection systemconfigured in accordance with one embodiment of the systems and methodsdescribed herein. Many of the embodiments described below are used fordetecting microorganism such as Cryptosporidium and Giardia; however, itwill be understood that the systems and methods described herein can beused to detect any particle capable of detection using the systems andmethods described, such as bacteria and yeasts. Bacteria are typicallysmaller than Cryptosporidium and Giardia ranging from 500 nanometersdiameter upwards to 2 microns and from oval to rod shape. Yeasts aretypically the size of Giardia or larger. Further, while the embodimentsdescribed below generally describe detected particles in water, it willbe understood that the systems and methods described can be used todetect particles and other liquids, and even in other media such as air.

System 100 comprises a light source 102 configured to provideillumination 104 to a target area 108. In the embodiment of FIG. 1,target area 108 is within a flow cell 106. Water intended to beinterrogated for various particles or microorganisms can flow throughflow cell 106, e.g., in a downward direction as indicated. Illumination104 will encounter particles in target zone 108, which will cause theillumination to scatter in a manner different than the illuminationtransmitted through the surrounding fluid medium.

System 100 can also comprise an optical system 124. Optical system 124can comprise several elements. For example optical system 124 cancomprise a lens, or lens system 112 as well as an optical element 114.The system 100 can also comprise a detector, detector system, ordetector array 116, which can be interfaced with a processing system118.

Light source 102 can be configured to deliver a structured lightpattern, or illumination. Thus, light source 102 can be, e.g., acoherent light source, such as a laser. Depending on the embodiment,light source 102 can comprise a single light source, such as a singlelaser, or a plurality of light sources, such as a plurality of lasers.Further, the wavelength of the light source can be at a fixedwavelength. Alternatively, when multiple light sources are used, thelight sources can have several discrete wavelengths.

Accordingly, light source 102 can be a laser configured to produce alaser beam 104. When laser beam 104 strikes a particle within targetarea 108, the particle will cause the beam to scatter in a pattern thatis different than the pattern produced due to beam 104 traveling throughthe water flowing in flow cell 106. Optical system 124 can be configuredto then pick up the scattered light and direct it onto detector 116.

Detector 116 can actually be a plurality of detectors, such as aplurality of detectors arrayed in different positions around target area108. Alternatively, detector 116 can comprise an array of photodetectors. For example, in one embodiment, detector 116 can actuallycomprise a linear array of photo detectors configured to detect thescattered light and generate an electrical signal having an amplitudecorresponding to the amplitude of the detected light. In oneimplementation, for example, a Charge Coupled Device (CCD) can be usedfor detector 116. CCDs are readily available with thousands of pixels,wherein each pixel can form an individual photo detector. In anotherimplementation for example, a 2 dimensional array of photodiodes oravalanche photodiodes of 64, 128, 256, or 512 total pixels can be usedto increase the total dynamic range of the detector as compared to aCCD.

Detector 116 can be configured to generate an electrical signal, orsignals, reflective of the light pattern incident on detector 116. Thesignals can then be provided to processing system 118 for furtheranalysis. As described above, processing system 118 can convert thesignals into a pattern using various algorithms 122. Processing system118 can also comprise the memory configured to store a plurality ofoptical signatures, or patterns 120 that are associated with variousparticles, or microorganisms of interest.

Thus, processing system 118 can compare the pattern generated usingalgorithms 122 to one of the stored patterns 120 in order to identifyparticles within target zone 108.

As mentioned above, algorithms 122 and patterns 120 can be used todetermine many features of particles being identified within target zone108, e.g., including the size, shape, internal structures or morphology,particle surface, and material composition, i.e., organic or inorganic.For example, certain embodiments can use Multiple Analysis Of Variance(MANOVA) algorithms, neuro-networks, simulated and annealing, algorithmindependent machine learning, physiologic, grammatical methods, andother algorithmic techniques for pattern generation and recognition. Itwill understood, however, that the systems and methods described hereinare not limited to any specific algorithms or techniques, and that anyalgorithm or technique, or a combination thereof, that could be used toperform the processes described herein can be used as required by aparticular implementation.

Particles within target zone 108 will cause light from laser beam 104 toscatter as illustrated in FIG. 1. Light scattering from target zone 108at an angle greater than 8 from the optical axis of beam 104 will beinternally reflected within flow cell 106 at the interface offlow cell106 with the external atmosphere. Thus, only light at angles less than 8can escape and be picked up by optical system 124.

In certain embodiments, a spherical lens (not shown) completelysurrounding the flow cell, except for the flow cell inlet and outlet,can be placed at the interface of flow cell 106 in order to allow lightscattered at any angle to the lens to pass through the lens to opticalsystem 124. Of course, including such a spherical lens increases thecomplexity and cost of system 100.

Light passing through target zone 108 along the optical axis of beam 104will generally be of a much greater intensity than that of the scatteredlight beams. The intensity of the beam along the optical axis can be sogreat that it can essentially prevent, or degrade detection of thescattered light beams. Accordingly, a beam stop 110 can be included inorder to deflect beam 104 and prevent it from entering optical system124 and being detected by detector 116.

The light scattered by a particle within target zone 108 can enteroptical system 124, which can comprise an optical element 114. Opticalelement 114 can be configured to direct the scattered light ontodetector 116. Specifically, optical element 114 can be configured insuch a way that it can direct light traveling along a given path to anappropriate position on detector 116 or to an appropriate detectorwithin an array of detectors comprising detector 116. For example, inone embodiment, optical element 114 can be a holographic optical elementconstructed so that each refracting section refracts, or redirects lightfrom one of the scattered paths so that it falls on the correct locationof detector 116. In other embodiments, optical element 114 can comprisea zone plate lens that can be configured to map the distance from thecentral optical access to a unique mapping that is useful for high speedscanning.

In certain embodiments, the scattered light may need to be collimatedafter it passes through target zone 108. Thus, a converging lens 112 canbe included in optical system 124. A converging lens can be configuredto reduce the angle spread for the various scattered light rays. Inother words, a converging lens can be configured to collimate orconverge the spread light rays. In other embodiments, some other opticaldevice can be used to collimate the scattered light rays. It will alsobe apparent, that certain embodiments may not need an optical lens 112,i.e., collimation may not be necessary depending on the embodiment.Thus, optical system 124 mayor may not contain an optical lens 112, or acollimator, as required by the specific implementation.

As mentioned above, detector 116 can actually comprise a plurality ofdetectors such as a linear detector array or 2 dimensional array such asa Charge Coupled Device (CCD) or for better dynamic range, a 2dimensional array of photodiodes or avalanche photodiodes. In oneembodiment, for example, detector 116 can actually comprise a linearphoto diode camera, e.g., a 128-pixel linear photo diode camera. Inanother embodiment, a square array of photodiodes may be used fordetector 116. In yet another embodiment, an array of photodiodesarranged in segmented concentric circles may be employed for detector116.

Certain embodiments take advantage of the low-cost and extremely highcomputing horsepower provided by the latest PC chips, operating systems,and software, along with a unique photodiode 2-dimensional array camerasystem. These embodiments can be optimized for the detection andclassification of microorganisms vs. other particles in water (typicallysilica), a process that is still difficult nonetheless. Microorganismscan range in size from 400 nanometers to 12 microns. By using the MIEcalculations from Philip Laven's program (found at www.philiplaven.com).a pioneer in this field, to generate scattered intensities, FIG. 1Aprovides a plot that shows that over 3 orders of magnitude in detectordynamic range is required for bacterias (400 nm to 2 micron range).

An exemplary embodiment of a 2-D camera that can be used in conjunctionwith the systems and methods described herein can be configured to use avery high-speed (frame rate) 2 dimensional photo-diode array to providehigh dynamic range, and limited pixel resolution to provide fastcomputer algorithms and high sensitivity. FIG. 1B illustrates 2-Dscatter patterns from various particles taken with a MALS systememploying a 2-D camera as disclosed herein. FIG. 1C illustrates anexemplary layout of a preferred embodiment of the 2-dimensionalphotodiode array. In this embodiment, there are 256 active elementsarranged in a 16×16 square grid. Each pixel is approximately 1.1 mmsquare and they are laid out on 1.5 mm center to center spacing.

Regardless of the type of detector 116 employed, optical element 114will be selected so as to complement detector 116 by directing thescattered light rays onto the appropriate pixel, or a section ofdetector 116; however, in certain embodiments, optical element 114 maynot be needed. For example, in certain embodiments, the scattered lightrays are incident directly onto detector 116.

FIG. 2 is a diagram of a particle detection system 200 that does notinclude an optical element. Thus, system 200 comprises a light source202, such as a laser, that produces a beam 204 that is incident onparticles in target zone 208 within a fluid flowing in flow cell 206.The particles scatter beam 204 and the scattered beams are then incidentdirectly on a detector 212. Detector 212 then produces electricalsignals based on the incident scattered light rays and provides theelectrical signals to processing system 214. Processing system 214 can,like processing system 118, be configured to generate a pattern from theelectrical signals using algorithms 218 and compare them against storedpatterns 216 in order to identify particles within target zone 208.

In the embodiment of FIG. 2, a beam stop 210 is still required toreflect the light ray traveling along the optical axis.

For example, in one embodiment, detector 212 can comprise a 64-pixeldetector array, while in other embodiments, detector 212 can comprise a128-pixel detector array. In certain embodiments, it can be preferredthat detector 212 comprise a 256-pixel detector. Arrays larger than256-pixels can be utilized in the present invention at a penalty ofincreasing cost and complexity. It should also be noted, that detector212 can comprise conditioning amplifiers, multiplex switches, anAnalog-to-Digital Converter (ADC) configured to convert analog signalsproduced by the detector pixel elements into digital signals that can bepassed to processing system 214. An example embodiment of a detector isdescribed in more detail below with respect FIG. 14.

Further, system 200 can include telescoping optics (not shown) in orderto collimate the scattered light rays if necessary.

As mentioned above, each type of particle, or microorganism, willscatter light giving off a unique pattern called an optical signature,or bio-optical signature. A detector, such as detector 212, can collectthe scattered light and capture the patterns. Electrical signalsrepresentative of the pattern can then be provided to a processingsystem such as processing system 214. FIGS. 3 and 4 illustrate exampleoptical signatures for two different types of particles.

FIG. 3A is a picture illustrating subtilis spores, a microorganism.FIGS. 3B and 3C are pictures illustrating the optical signatureassociated with the subtilis spores of FIG. 3A. FIG. 4A is a pictureillustrating a ball of plastic spheres. FIGS. 4B and 4C are diagramsillustrating the optical signature for the ball of plastic spheres inFIG. 4A. Thus, the optical signatures, or patterns, of FIGS. 3A-3C and4A -4C, which can be produced using, e.g., algorithms 218, can becompared to patterns stored within the processing system.

As noted above, if some form of spherical lens, or other device, is notused, then only scattered light rays with an angle less the e would bedetected; however, if the illumination beam is incident at an angle,then light can be measured through twice the original measuredscattering angles and still be captured by the detector. The scatteringangle of the scattered radiation is inversely proportional to the sizeof the feature or object from which it was scattered, thus smallerfeatures scatter light into larger angles. Illuminating the sample atangle permits radiation scattered from smaller features to still becaptured by the detector's optical system; thus, a greater resolutioncan be achieved. This is illustrated by FIGS. 5-7.

When illumination is incident upon a particle 502 along an optical axis504, vector k_(i) can be used to represent the illumination. Asillumination incident along vector k_(i) encounters particle 502, itwill be scattered through a sphere of 360 degrees but only detectedthrough a range of angles up to Θ. Thus, a scattered light ray at theouter edge of the detector range can be represented by vector k_(s).

If, however, the illumination is incident at an angle illustrated byvector k_(i) in FIG. 6, then the detector will be able to see lightscattered through a greater range of angles. For example, the scatteredlight rays will be measured through an angle of 2Θ. As a result,objective 500 can collect scattered light rays scattered through twicethe angle as compared to the system in FIG. 5. Thus, the resolution ofthe system illustrated in FIG. 6 would be twice that of the systemillustrated in FIG. 5.

FIG. 7 is a diagram illustrating that the same effect can be achievedusing a plurality of incident beams 508 that include beams incident atan angle from above and below the optical axis 504. Switching on or offthe individual laser beams can provide additional multiple angleswithout having to provide additional detectors. If the switching is fastenough compared to the transit of the particle through the beam, thenthe additional angles can be obtained for the same particle.

It should be noted that objective 500 in FIGS. 5-7 can be a zone plateas well as another conventional optical element, including a holographicoptical element.

FIGS. 8 and 9 illustrate that the technique depicted in FIGS. 6 and 7could be achieved by altering the position of the optical detector or byconfiguring the light source so that the illumination is incident at anangle upon the target zone. Thus, FIG. 8 is a diagram illustrating anexample particle detection system 800 in which an optical detector 812has been repositioned so as to capture scattered light rays scattered toan angle 2Θ. In FIG. 8, a light source 802, such as a laser, produces abeam 804 that is incident on particles within target zone 808. It shouldbe noted that a beam stop 810 can still be required within system 800 todeflect the beam traveling along the optical axis.

It will be understood that system 800 can comprise a processing system,but that such system is not illustrated for simplicity.

FIG. 9 is a diagram illustrating an example particle detection system900 in which optical source 902 is configured such that beam 904 isincident upon target zone 908 at an angle equal to or greater than thecritical angle defined by the phenomenon of total internal reflection.In the system of FIG. 900, by selecting the incident angle such that thebeam experiences total internal reflection, the beam 904 is internallyreflected within flow cell 906, and thus a beam stop is not required.This can lower the cost and complexity of system 900 and can, therefore,be preferable.

Again, it will be understood that system 900 can comprise a processingsystem, but that such system is not illustrated for simplicity.

As mentioned above with respect to FIG. 1, angles larger than Θ will bereflected internally within flow cell 106. In general, collecting highangle scattered light from an object in a liquid medium requires somemechanism to prevent the internal reflection of the high angles beingsought. This problem can be referred to as Total Internal Reflection(TIR) of the high-angle scattered light. TIR can occur at high to lowindexes of refraction interfaces within the optics of the instrument orsystem being used to observe or collect the scattered light, e.g., theinterface between flow cell 106 and the external atmosphere.

In certain embodiments, a second surface curved mirror reflecting opticcan be used to collect and reflect the light. Such an optic can alloweasy capture of light angles up to 90° for all azimuthal angles, whenthe sample is index coupled with the non-reflecting surface of thecollection optic. Such an optic can prevent TIR issues at angles greaterthan approximately 40°.

FIG. 10 is a diagram illustrating a scatterometer ray trace for lightscattered by a particle and collected using a second surface curvedmirror 1004. In the example of FIG. 10, light reflected through an angleof 60° by the reflective surface of mirror 1004 corresponds to lightscattered through an angle of 90° by object 1002. The scattered light1008 passes by beam stop 1006, which is configured to reflect the highintensity light traveling along the beam axis. Scattered light can thenbe incident on a detector surface 1010, such as a CCD or a 2-D cameraarray as described above.

FIG. 11 is a diagram illustrating a pattern produced by scattered light1008 incident on detector 1010. The pattern depicted in FIG. 11corresponds to the diffraction pattern generated by a sphere comprisinga diameter of approximately 8 microns. Line 1102 is drawn along thelaser polarization axis. Beam stop 1006 reflects light along the beamaxis.

FIG. 12 is a graph illustrating the relative intensity of scatteredlight versus the scatter angle for the pattern of FIG. 11. As can beseen, light scattered through an angle of 90° can be detected usingoptic 1004.

Thus, for example, a reflective optic, such as optic 1004 can beincluded in systems such as systems 100 and 200. An optic such as optic1004 can be included in place of, or in addition to other optics with inthe system. This can increase the angle 8 through which scattered lightcan be collected and detected. Although, systems 100 and 200 are justexamples of the types of systems that can make use of a second surfacecurved mirror for collecting and detecting high-angle scattered light asdescribe above. Accordingly the embodiments described with respect toFIGS. 10-12 should not be seen as limited to implementation in systemssuch as systems 100 and 200.

For example, FIG. 13 is a diagram illustrating a system 1300 configuredto collect light scattered by a particle and reflected by a curvedreflective optic as described above. System 1300 comprises a laser 1302configured to generate a laser beam 1304. Beam 1304 can be directed at a45 degree reflective silver prism 1306, which can cause beam 1304 to gothrough interface optic 1308, flow cell 1310, and reflective optic 1312through unsilvered area 1314 on reflective optic 1312. Thus, silverprism 1306 and unsilvered area 1314 on reflective optic 1312 allow beam1304 to be removed from the desired signal, much as beamstop 1006 (seeFIG. 10) does in alternative embodiments.

Interface optical element 1308 can be a separate element opticallycoupled to flow cell 1310 with a coupling medium, or integral to thedesign of the flow cell 1310. Reflective optical element 1312 can alsobe a separate element optically coupled to flowcell 1310 with a couplingmedium or integral to flowcell 1310. The scattered radiation patternproduced by an object in flowcell 1310 is reflected by reflectiveoptical element 1312. The reflected light then falls on the2-dimensional photo detector array 1316.

FIG. 14 is a diagram illustrating an example detector system 1400, suchas detector 212 or a system including array 1316. In the example of FIG.14, system 1400 comprises a 256-pixel detector packaged array 1402removably attached to a signal conditioning and digitizing board 1430.Board 1430 can comprise signal conditioning amplifiers 1406, 1408 and1412, multiplex analog switches 1404 and 1414, a 14-bit Analog toDigital Converter (ADC) 1410, a microcontroller 1418, and a USB2.0communications chip 1418. Thus, such a system 1400 can be packaged as acomplete high-speed USB 2.0 camera operating at frame rates of 1,000frames per second upwards to 10,000 frames per second. Normally eachpixel (photodiode) is connected directly to a trans-impedance amplifier1406. A unique aspect of the disclosed 2-D camera technique is that only16 total trans-impedance amplifiers (1406) are required to operate theentire photodiode array 1402 instead of 256 trans-impedance amplifiers,as is required in conventional designs. By using a low-noise analogmultiplexer (MUX) directly to select one of 16 pixels to send to one ofthe trans-impedance amplifiers 1406, only 16 MUXs are required alongwith only 16 trans-impedance amplifiers 1406.

While the invention has been described with respect to a limited numberof embodiments, the specific features of one embodiment should not beattributed to other embodiments of the invention. No single embodimentis representative of all aspects of the inventions. Moreover, variationsand modifications therefrom exist. For example, the magnetic memorydevices and methods of storing data described herein can be used in anycircuit using circuit design tools. In some embodiments, the devices aresubstantially free or essential free of any feature on specificallyenumerated herein. Some embodiments of the method described hereinconsist of or consist essentially of the enumerated steps. The appendedclaims intend to cover all such variations and modifications as fallingwithin the scope of the invention.

1. A system for detecting and identifying a particle in a liquid, thesystem comprising: a target zone comprising a liquid medium, theparticle carried into the target zone by the liquid medium; a lightsource configured to generate a light beam and to direct the light beamthrough the target zone; an optic configured to collect and reflectlight scattered by a particle in the target zone, the optic comprising areflective optic having a curved reflecting surface, the reflectiveoptic coupled with the liquid medium in the target zone, the reflectiveoptic configured to collect and reflect light scattered by a particle inthe liquid medium in the target zone; and a 2-dimensional detectorcamera configured to detect the reflected light.
 2. The system of claim1, wherein the 2-dimensional detector camera provides a frame rate fromabout 1000 frames per second to 10000 frames per second.
 3. The systemof claim 1, wherein the 2-dimensional detector camera comprises a squarearray of photodiodes.
 4. The system of claim 3, wherein the square arrayof photodiodes comprises 256 active elements arranged in a 16×16 squaregrid.
 5. The system of claim 4, wherein each of the 256 active elementscomprises a size of approximately 1.1 mm².
 6. The system of claim 5,wherein the 256 active elements comprise a layout having about 1.5 mmcenter-to-center spacing between elements.
 7. The system of claim 3,wherein the 2-dimensional detector camera further comprises a signalconditioning and digitizing board connected to the array of photodiodes.8. The system of claim 7, wherein the board comprises a plurality oftrans-impedance amplifiers, wherein a plurality of photodiodes areconnected to each trans-impedance amplifier.
 9. The system of claim 8,wherein each of the pluralities of photodiodes are connected to theirrespective trans-impedance amplifier via a multiplexer.
 10. The systemof claim 1, wherein the reflective optic is a second surface curvedmirror.
 11. The system of claim 10, wherein the reflective optic allowslight scattered through an angle of 90° to be captured by the detector.12. The system of claim 1, further comprising a beam stop configured todeflect the light beam after it has passed through the target zone. 13.A system for detecting and identifying a particle in a liquid, thesystem comprising: a flowcell comprising a flowing liquid media and atarget zone, the particle carried in the path of a light beam by theliquid media; a light source configured to generate the light beam anddirect the light beam through the target zone; an interface optic; areflective optic configured to collect and reflect light scattered by aparticle carried by the liquid media through the target zone, the opticcomprising a reflective optic having a curved reflecting surface, thereflective optic coupled with the liquid medium in the target zone, thereflective optic configured to collect and reflect light scattered by aparticle in the liquid medium in the target zone; and a 2-dimensionaldetector camera configured to detect the reflected light.
 14. The systemof claim 13, wherein the 2-dimensional detector camera provides a framerate from about 1000 frames per second to 10000 frames per second. 15.The system of claim 13, wherein the 2-dimensional detector cameracomprises a square array of photodiodes.
 16. The system of claim 13,wherein the interface optic is integral to the flowcell.
 17. The systemof claim 13, wherein the reflective optic is integral to the flowcell.